Tire Size 285 vs 305
 

I just found something interesting on Pepboys web site they have a formula to determine tire size and when you do the calculations of a 285/75/16 and the 305/70/16 both tires come out to be the same as far as how tall they are here is the formula on there site.




(Cross section width x 0.aspect ratio) x 2
__________________________________ + Wheel Diameter
25.4

=Overall Tire diameter in inches



EXAMPLE: 285 x 0.75 x 2
_____________ +16 inches =32.83
25.4

Basically your correct.

(16' Tire Size Comparison)
285/75-16 is about 33x11.5-16
and
305/70-16 is about 33x12.5-16

If anyone is interested 17's are similar.

(17' Tire Size Comparison)
285/70-17 is about 33x11.5-17
and
305/70-17 is about 33x12.5-17

Yep, all passenger tires are a just a math calculation to determine size. I get half a millimeter off on the diameter between the two.

rkjerue, 285/70R17 and 305/70R17 are not similar like you said. Use his formula to calculate it.

285/7017 = 32.7" diameter
305/70R17 = 33.8" diameter

APT you are incorrect because you got the size of the 285 wrong it is not a 285/70/16 but a 285/75/16 which makes them the same size try your calculations again useing the right numbers and you will see for yourself.

Richard D.:beers:

Richard, the 16" example is correct.

285/70R16 = 265/75R16

This one is wrong, or at least, that there is about an inch in diemter difference. If a 265/75R17 tire existed, it would be similar to 285/70R17.

OK APT i now se what you are talking about he got the 285/70/17 part wrong thus creating the wrong eqaution Good enough. MY BAD and I stand corrected.The thing is I was not talking about 17" tires and haven't even looked at any of the sizes that are available but as far as 16" tires goes i think there may be a 265/75/16 available.I would have to look it up and check.And since i have not need for a 17" tire i do not pay attention to what is available for that size.

Richard D.:thumbsup: